Electronics Notes .. by Assistant Professor Raghavendra Singh Kushwah[Rajawat] NRIITM,Gwalior, M.P.,India These are valuable and important engineering notes for students of BE,Diploma,AMIE in branches of Electronics and communication/Electronics and instrumentation/Electrical\Electronics engineering, as cathode ray oscilloscopes,function generators,multimeter s, power-supply, transducer based measurements,electronics components diodes, transistors sensors and transducers,.......

Saturday, 10 December 2011

Introduction to Analog and Digital MULTIMETERs

MULTIMETER

Multimeters may use analog or digital circuits—analog multimeters (AMM) and digital multimeters (often abbreviated DMM or DVOM.) Analog instruments are usually based on a microammeter whose pointer moves over a scale calibrated for all the different measurements that can be made; digital instruments usually display digits, but may display a bar of a length proportional to the quantity being measured.A multimeteris an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current and resistance. it is also known as a VOM (Volt-Ohm meter).

Digital multimeters: In a digital multimeter the signal under test is converted to a voltage and an amplifier with electronically controlled gain preconditions the signal. A digital multimeter displays the quantity measured as a number, which eliminates parallax errors.

Block diagram:

Analog multimeters:Analog multimeters are common; a quality analog instrument will cost about the same as a DMM. Analog multimeters have the precision and reading accuracy limitations described above, and so are not built to provide the same accuracy as digital instruments.

A multimeter can be a hand-held device useful for fault finding and field service work ,which can measure to a very high degree of accuracy. They can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as electronic equipment, motor controls, domestic appliances, power supplies, and wiring systems.

multimeters can measure many quantities as,Voltage, alternating and direct, in volts.Current, alternating and direct, in amperes.Resistance in ohms.

Additionally, some multimeters measure:Capacitance in farads.Conductance in siemens.Frequency in hertz.Inductance in henrys.Temperature in degrees Celsius or Fahrenheit, with an appropriate temperature test probe, often a thermocouple.

Digital multimeters may also include circuits for:Continuity; beeps when a circuit conducts.Diodes (measuring forward drop of diode junctions, i.e., diodes and transistor junctions) and transistors (measuring current gain and other parameters).Battery checking for simple 1.5 volt and 9 volt batteries. This is a current loaded voltage scale. Battery checking (ignoring internal resistance, which increases as the battery is depleted), is less accurate when using a DC voltage scale.Various sensors can be attached to multimeters to take measurements such as:Acidity/Alkalinity(pH)Wind speedRelative humidityLight level